Circuit breaker with loosely coupled deenergizing means for high overload currents

ABSTRACT

Disclosed is a circuit breaker in which the current-carrying contacts are mechanically opened in response to a delay induced solid state switch. The line current passes through the primary of a transformer which is mounted on a common core with the transformer secondary and a third winding. The third winding is energized by the switch to open the breaker contacts. High overload currents are coupled directly from the transformer to the breaker mechanism bypassing the delay. Also provided is a ground fault circuit for closing the switch when the line becomes unbalanced.

United States Patent [72] Inventors David H. Wilson, Cambridge,

Lyal N. Merriken, Cambridge; John R. Shand, Easton, Md.

[21] Appl. No. 808,175

[22] Filed Mar. 18, 1969 [45] Patented Feb. 23, 1971 [73] Assignee Airpax Electronics Incorporated Cambridge, Md.

[54] CIRCUIT BREAKER WITH LOOSELY COUPLED DEENERGIZING MEANS FOR HIGH OVERLOAD CURRENTS 6 Claims, 2 Drawing Figs.

[51] Int. Cl. H02h l/02 [50] FieldofSearch 3l7/33,27,

[56] References Cited UNITED STATES PATENTS 3,187,225 6/1965 Mayer 317/26 3,376,477 4/1968 Weinger 317/27 3,440,580 5/1969 Molenaar 335/18 3,467,890 9/1969 Mayer 317/33 3,473,091 10/1969 Morris et al. 317/18 Primary Examiner-D. F. Duggan Assistant Examiner-Ulysses Weldon Att0rneyLe Blanc and Shur I l l |8--:: I I ""1 I I l LOAD I l L J l l I I I Wrens I I I I J 28 76 I' F I 6.8K 96 I 64 0 I ?0 fe 1 39K 74 6B c4302: W I I 68 c5 I J y g 5 I,

"PATENTED mm mm 3566189 SHEET 2 11F 2 NVENTORS H. WILSON LYA .MERRIKEN J0 SHAND ATTORNEYS CKRCUHT BREAKER WITHLOOSELY COUPLED DEENERGHZHNG MEANS FOR HIGH OVERLOAD CURRENTS This invention relates to 'a circuit breaker incorporating an inverse delay and more particularly to an electronic magnetic circuit breaker incorporating solid state delay and ground fault protection.

Circuit breakers are well known and are used in a variety of applications to protect against overload currents and leakage currents. These include both thermal and magnetic breakers, as well as breakers utilizing magnetic/hydraulic and solid state delay mechanisms. However, insofar as applicants are aware,

none of the prior constructions utilize the mechanical opening of current-carrying contacts with delay induced solid state switching devices.

The present invention is directed to an improved circuit breaker incorporating an inverse time delay in conjunction with mechanical opening of contacts for positive circuit interruption. The circuit breaker combines the positive opening of the contacts with the advantages of temperature compensated inverse time delay, making it possible to provide the analogue of the circuit protected more closely than with previous breakers. ln the present invention, high current overloads operate on a magnetic principle and bypass the solid state circuitry. Also included in the unit is a ground fault protection circuit that does not interfere with the nonnal operation of the breaker.

In the device of the present invention, the line current is passed through the primary of a transformer which is loosely coupled to the armature of a circuit breaker trip mechanism so that the circuit breaker remains latched for normal line currents. The transformer is provided with a secondary winding connected to a solid state switch through an electrical delay which provides inverse delay tripping of the circuit breaker. When the solid state switch is closed, a third transformer winding is energized, actuating the armature of the breaker and opening the circuit after a predetermined and variable delay.

By loosely coupling the transformer primary to the circuit breaker armature, normal currents through the line do not produce magnetic tripping but excessive overloads effect sufficient coupling to the circuit breaker armature to provide mechanical trip bypassing the solid state delay. Also incorporated in the circuit is a differential transformer coupled through a differential amplifier to the solid state switch which is energized when the line becomes unbalanced due to ground fault currents. ln this way, ground fault protection is provided to trip the circuit breaker independently of the overload and delay protection.

It is therefore one object of the present invention to provide an improved circuit breaker device.

Another object of the present invention is to provide an improved circuit breaker which combines mechanical opening of contacts for positive current interruption with an inverse time delay.

Another object of the present invention is to provide a circuit breaker having overload protection in combination with a solid state time delay switch.

Another object of the present invention is to provide a circuit breaker having-incorporated therein ground fault protectron.

Another object of the present invention is to provide an electronic magnetic circuit breaker incorporating solid state delay and ground fault protection in a single housing or package.

These and further objects andadvantages of the invention will be more apparent upon reference to the following specification. claims, and appended drawings, wherein:

FIG. 1 is a circuit diagram showing the novel circuit breaker of the present invention incorporating both solid state delay and ground fault protection; and

FIG. 2 is a cross section through the circuit breaker showing the details of the tripping transformer construction.

Referring to the drawings, the circuit breaker of the present invention is generally indicated at 10 in FIG. 1 and is shown as contained within a housing or jacket indicated by the dashed box 12. The output from the circuit breaker 10 is by way of powerline leads l4 and 16 to a load device, indicated in dashed lines at 18, which load is to be protected by the circuit breaker. The load is indicated in dashed lines to show that it may be positioned either at the site of the circuit breaker or may be remotely located from the breaker.

Power is applied through circuit 10 to the load 18 from a powerline source, indicated by dashed lines 20, which source may be at the site of the circuit breaker or remotely located. By way of example only, the source may be a conventional AC power main supply supplying power to the load by way of input sections 22 and 24 of a pair of ungrounded powerlines, labeled L, and-L respectively. These lines are connected to the interior of housing 12 and passthrough a differential transformer, generally indicated at 26, and labeled T Transformer 26 is provided with a toroidal core and lines L, and 1., pass through the core and form single turn primary windings to produce a differential output on the secondary winding 28 of toroid transformer 26. The primary leads are drawn through the core in the same direction and the secondary 28 preferably is wound with about 250 turns. The differential toroidal core transformer 26 provides for ground fault detection in a manner more fully described below.

Powerline L, is also connected to the primary 32 of a second transformer, generally indicated at 30, labeled T,. ln addition to primary winding 32, having turns N,, transformer 30 is provided with two additional windings 34 and 36, with turns N and N respectively. Winding 34 is connected to the opposite sides of a fullwave rectifier bridge 38 comprising rectifier diodes CR,, CR CR and CR The fullwave rectified output from the bridge 38 is fed by way of leads 40 and 42 to a filter capacitor 44, labeled C,, and to a time constant circuit or inverse delay circuit 46 comprising a variable resistor 48, labeled R,, and a second capacitor 50, labeled C Capacitor 50 is connected through a blocking rectifier diode 52 to the gate 54 of a solid state switch in the form of a silicon controlled rectifier 56, labeled 0,. Switch 56 is connected in series with winding 36 of transformer 30 across the line. When winding 36 is energized, circuit breaker switches 58 and 60 in the powerline are opened. These switches are mechanically ganged together as indicated by the dashed lines at 62.

The secondary 28 of differential transformer 26 is connected through a coupling capacitor 64, labeled C to a differential amplifier 66, which differential amplifier includes capacitor 68, labeled C The output of the differential amplifier passes through a coupling capacitor 70, labeled C and through a rectifier diode 72 and resistors 74 to the gate 54 of the SCR switch 56. The other input of the differential amplifier is connected by lead 76 to line L,,.

Connected across the lines L, and L by way of lead 78,

rectifier diode 80, and a filter 82 comprising series resistor 84' and shunt capacitor 86, is a Zener diode 88. Diode 88 acts as a voltage regulator supplying a regulated voltage to the gate 92 of a field effect transistor also having a drain electrode 93 and source 94. Field effect transistor 90 is labeled Q, and its drain-source circuit is connected across capacitor 50. Finally, the junction of the upper plate of capacitor 86 and Zener diode 88 is connected to differential amplifier 66 by way of lead 96.

FIG. 2 is a cross section through the casing 12 showing some of the details of the circuit breaker and, in particular, the details of the transformer 30. The mechanical portions of the circuit breaker are of conventional construction and in addition to the casing 12, the breaker includes a handle 98 connected to a collapsible toggle mechanism, generally indicated at 100, to move a contact bar 102 carrying movable contact 104 which is adapted to engage a stationary contact 106 completing powerline L, from its input 22 to its output 14. As

indicated in FIG. 2, contacts 104 and 106 form the switch 58 of FIG. 1 and it is understood that these contacts are mechanically coupled to similar contacts forming the switch 60 of FIG. 1 for opening the circuit in the second line L The mechanical construction of the circuit breaker may be of any conventional type and, in the preferred embodiment, takes the form shown and described in assignees Pat. No. 3,412,351 or copending application Ser. No. 682,081, filed Nov. 13, 1967, which are incorporated herein by reference.

The input section 22 of line L, is connected by way of a short lead 108 to the primary winding 32 of the transformer 30. This winding, along with windings 34 and 36 illustrated in FIG. 2, are wound about a magnetic core 110 having its center drilled out for a portion of its length as indicated at 112 adjacent the end of armature 114. The other end of coil 32 is connected by the flexible braided wire 116 to the contact bar and is in electrical communicationfthrough this contact bar with the movable contact 104. Armature 114 forms part of a bell crank lever and when drawn toward the pole surface 118 of the core, operates a trip mechanism forming a part of the toggle 100 in a well known manner to collapse the toggle and cause the movable contact 104 to move away from the stationary contact 106, thus opening switch 58. At the same time, the mechanically linked switch 60 of FIG. 1 is also opened.

The toggle automatically resets andlthe switches may be reclosed by manual operation of the handle 98.

OPERATION OF THE clRcUiT BREAKER AT R BELOW THE RATED cURRENT. or THE BREAKER WITHOUT THE PRESENCE OF GROUND FAULT CURRENT Line voltage is applied to the input ends 22 and 24 of lines L, and L and current flow is through powerline L, and the primary winding 32 of transformer 30. The current flow can be further traced through the breaker switch 58, load 18, switch 60 in the other side of the line, backto the input end 24 of line L,,. Lines L, and L physically pass through the toroidal core of transformer 26 where eachforrns a single turn primary winding for this transformer.

When ground fault leakage current does not flow, there is no signal from the secondary of transformer 26 since the current flow through line L, is canceled by the exact amount of flow in the opposite direction through line L,. A voltage is produced in secondary winding 34 of transformer 30. This voltage is rectified in bridge 38 and applied to the network consisting of capacitor 44, variable resistor 48, and capacitor 50. Capacitor 44 is provided to filter high frequency voltage transients and to avoid nuisance tripping. Resistor 48 and capacitor 50 form the delay circuit 46 which provides an adjustable time constant to govern the time that it takes the voltage across capacitor 50 to rise and trip SCR 56 via diode 52 and gate 54. In the case considered (line current at or below rated breaker current), the voltage never reaches the firing point of SCR 56. The voltage level to delay network 46 is determined by the ratio N /N, of transformer 30.

ground fault current does not flow, the protection circuits do not function and switches 58 and 60 remain closed.

OPERATION ABOVE RATED CIRCUIT BREAKER CURRENT WITHOUT PRESENCE or GROUND FAULT CURRENT When excessive current flows through winding 32 of transformer 30, a voltage is produced by secondary winding 34 which, after rectification, causes SCR 56 to conduct. When the SCR turns on, full line voltage is applied to winding 36 of transformer 30. The current which flows through winding 36 operates armature 114 (FIG. 2) which in turn trips the toggle and opens both sets of contacts 58 and 60 of the breaker. Delay network 46 determines the time required for the voltage to gate 54 of the SCR to rise to the level required to turn it on. Resistor 48 is made adjustable to permit varying the inverse time delay as required.

When the breaker contacts open, bias voltage is removed from FET causing this transistor to become conductive and allowing capacitor 50 to discharge through it. This provides equal trip times for successive breaker openings since it allows capacitor 50 to start charging from zero volts each time the breaker is switched on. With power on and the breaker energized, FET 90 is effectively an open switch due to the approximately 10 volts applied to its'gate, 92. When the gate potential goes to zero with the opening of breaker switches 58 and 60, transistor 90 becomes a low resistance between drain and source discharging capacitor 50. 4

OPERATION AT OR BELOW RATED BREAKER CURRENT WITH THE PRESENCE OF GROUND FAULT CURRENT When a leakage current of approximately 50 milliamps or more exists from load 18 to ground, an unbalance in current flow between lines L, and L occurs. Since there is an unbalance, a voltage output is produced onthe secondary winding 28 of differential transformer 26. This AC signal voltage is coupled to differential amplifier 66 through coupling capacitor 64. Capacitor 68 forms part of amplifier 66. The output of the amplifier is connected through coupling capacitor 70, rectified by diode 72, and current limited by resistor 74 and applied to gate 54 of SCR 56 to cause the SCR to conduct. Again, when SCR 56 conducts, full line voltage is placed across winding 36 of transformer 30 causing the breaker mechanism to trip as previously described. Diode 52 acts as a blocking diode to provide independent action of the ground fault circuit and the current overload trip circuit.

OPERATION AT VERY HIGH CURRENT OVERLOADS The turns N,, N,, and N of windings 32, 34, and 36 are wound on the same =solid iron core (FIG. 2) and therefore the flux generated by current flowing in winding 32 is coupled directly to the armature 114. of the breaker. However, this coupling of the flux is very loose due to the fact that the iron core has the hole 112 drilled partway into it from the armature end of the core. At current overloads under about 600 percent of normal breaker ratings, this flux coupling is not sufficient to trip the breaker and operation of the time delay circuit or the ground fault circuit must take place to energize winding 36 to trip the breaker. However, when a severe short circuit in the load causes an overload above about 600 percent of rated current, the flux coupled to armature 14 from winding 32 is sufficient to cause instantaneous operation of the armature and tripping of the breaker without energization of winding 36 due to the closure of the SCR switch 56 by either the inverse delay circuit or the ground fault circuit.

It is apparent from the above that the present invention provides an improved circuit breaker which combines many features in a single small package of relatively simplified construction. It insures positive mechanical opening of the contacts for circuit interruption in combination with inverse time delay and incorporates as part of the unit ground fault protection, Selection of the inverse time delay desired is accomplished by simply changing the value of the components such as by varying the resistance of variable resistor 48. The delay is insensitive to the mounting position of the breaker and the breaker evidences higher shock and vibration capabilities than hydraulic/magnetic mechanisms (approximately two times the shock capabilities). The inherent temperature compensation provides equal trip characteristics over the entire operating range and instant tripping without delay is provided for overloads above about 600 percent to 800 percent of rated current or at almost any preset overload desired. Instant reset of the delay mechanism occurs after tripping as opposed to thermal breakers which require up to one minute to restore tripping characteristics and magnetic/hydraulic types which require up to about ten seconds. The unit exhibits increased tolerance to short duration, high amplitude current pulses that would cause nuisance tripping of magnetic/hydraulic type units. Finally, the ground fault detector insures against damage by unbalanced currents of either electrical machinery or human life. The ground fault detector can operate to break the circuit in about milliseconds and can have a sensitivity to ground fault currents of as little as milliamps.

We claim: I

l. A circuit breaker comprising a pair of contacts, a transformer having its primary coupled in series with said contacts, means including a collapsible toggle for opening and closing said contacts, a solid state switch coupled to the secondary of said transformer, the windings of said transformer being loosely coupled to said toggle whereby said toggle is collapsed only in response to excessive overload currents passing through said transformer primary, a third winding more tightly coupled to said toggle, and means coupling said switch to said third winding whereby said third winding acts to collapse said toggle when said switch is closed.

2. A circuit breaker according to claim 1 including an adjustable RC delay circuit coupling the secondary of said transformer to said switch.

3. A circuit breaker according to claim 2 wherein said transformer primary and secondary and said third winding are wound about a common core, said core having a hollow portion at its end adjacent said toggle.

4. A circuit breaker according to claim 2 including a second solid state switch coupled to said delay circuit for discharging said delay circuit when said contactsare opened.

5. A circuit breaker according to claim 2 including a ground fault circuit having its output coupled to said switch, said ground fault circuit comprising a toroidal transfonner having a pair of single turn primary windings, and a difierential amplifier and rectifier coupling said toroidal transformer to said switch.

6. A circuit breaker according to claim 1 including two pairs of contacts forming a pair ofcircuit breaker switches, said switches being mechanically ganged for simultaneous operation. 

1. A circuit breaker comprising a pair of contacts, a transformer having its primary coupled in series with said contacts, means including a collapsible toggle for opening and closing said contacts, a solid state switch coupled to the secondary of said transformer, the windings of said transformer being loosely coupled to said toggle whereby said toggle is collapsed only in response to excessive overload currents passing through said transformer primary, a third winding more tightly coupled to said toggle, and means coupling said switch to said third winding whereby said third winding acts to collapse said toggle when said switch is closed.
 2. A circuit breaker according to claim 1 including an adjustable RC delay circuit coupling the secondary of said transformer to said switch.
 3. A circuit breaker according to claim 2 wherein said transformer primary and secondary and said third winding are wound about a common core, said core having a hollow portion at its end adjacent said toggle.
 4. A circuit breaker according to claim 2 including a second solid state switch coupled to said delay circuit for discharging said delay circuit when said contacts are opened.
 5. A circuit breaker according to claim 2 including a ground fault circuit having its output coupled to said switch, said ground fault circuit comprising a toroidal transformer having a pair of single turn primary windings, and a differential amplifier and rectifier coupling said toroidal transformer to said switch.
 6. A circuit breaker according to claim 1 including two pairs of coNtacts forming a pair of circuit breaker switches, said switches being mechanically ganged for simultaneous operation. 